Re: [patch 57/60] x86/mm/kpti: Add Kconfig

[Andy Lutomirski]

On Mon, Dec 4, 2017 at 6:08 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>
> Finally allow CONFIG_KERNEL_PAGE_TABLE_ISOLATION to be enabled.
>
> PARAVIRT generally requires that the kernel not manage its own page tables.
> It also means that the hypervisor and kernel must agree wholeheartedly
> about what format the page tables are in and what they contain.
> KERNEL_PAGE_TABLE_ISOLATION, unfortunately, changes the rules and they
> can not be used together.
>
> I've seen conflicting feedback from maintainers lately about whether they
> want the Kconfig magic to go first or last in a patch series.  It's going
> last here because the partially-applied series leads to kernels that can
> not boot in a bunch of cases.  I did a run through the entire series with
> CONFIG_KERNEL_PAGE_TABLE_ISOLATION=y to look for build errors, though.
>
> [ tglx: Removed SMP and !PARAVIRT dependencies as they not longer exist ]
>
> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: keescook@xxxxxxxxxx
> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
> Cc: moritz.lipp@xxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
> Cc: hughd@xxxxxxxxxx
> Cc: daniel.gruss@xxxxxxxxxxxxxx
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: michael.schwarz@xxxxxxxxxxxxxx
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: richard.fellner@xxxxxxxxxxxxxxxxx
> Link: https://lkml.kernel.org/r/20171123003524.88C90659@xxxxxxxxxxxxxxxxxx
>
> ---
>  security/Kconfig |   10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> --- a/security/Kconfig
> +++ b/security/Kconfig
> @@ -54,6 +54,16 @@ config SECURITY_NETWORK
>           implement socket and networking access controls.
>           If you are unsure how to answer this question, answer N.
>
> +config KERNEL_PAGE_TABLE_ISOLATION
> +       bool "Remove the kernel mapping in user mode"
> +       depends on X86_64 && JUMP_LABEL

select JUMP_LABEL perhaps?

> +       help
> +         This feature reduces the number of hardware side channels by
> +         ensuring that the majority of kernel addresses are not mapped
> +         into userspace.
> +
> +         See Documentation/x86/pagetable-isolation.txt for more details.
> +
>  config SECURITY_INFINIBAND
>         bool "Infiniband Security Hooks"
>         depends on SECURITY && INFINIBAND
>
>